An article in the Nov. 25th recent issue of the NYT, "Rust-Free Reality: Creating an All-New Classic," talks about the growing business of supplying low-volume steel body panels to the restoration market. I've been curious for a long while about what they're using for dies, and what the processes are. As most of you know, making original dies for high-volume car manufacture costs millions of dollars for each die.
Before I start spending time on it, does anyone know the story about these steel panels?
I know little or nothing about the industry, but I recall reading about a fellow that was making repro tanks for old Brit bikes. He was making his press dies out of concrete.
Dunno if something similar is being done for limited run body panels.
It would definately speed things up to have a panel to use as a master, rather than building the die from scrtach, I'd think.
Some where around here, I have a copy of the ASTME collected papers from
1962.
There was an article about using steel filled epoxy for short run draw dies. They were making the same sort of panels. They were aluminum aircraft panels, if I recall correctly, but I imagine the state of the art has advanced in the last 45 years.
Some of them are original dies , believe it or not . The big three are notorious fior never throwing these things away, there is a warehouse near me full of injection moulds that are for chryslers not made since the mid eighties
Modern manufacturing has reduced costs for stamping dies to a fraction of what is once was , that and the newer grades of steel that can undergo multiple stampings without cracking or needing to be annealed
They were still forming aluminum with filled-epoxy dies when I was writing about it, around 1980. But superplastic aluminum was just coming in then and attention shifted to the new material.
Other posters have mentioned concrete and Kirksite, both of which have been used for steel forming that didn't require either a lot of precision or a lot of specific force. But my feeling is there must be something better these days, and these replacement-panel makers are using it.
We'll see. Maybe someone here has looked into the industry.
I remember the first story I read about that business, back around 1980, when someone had acquired original dies for a mid-'50s Chevy. It sounds from the NYT article, though, like the newer firms in the business are using something else.
All of which makes sense, but is that what they're using? Or are they using entirely different materials? The cost of just the block of steel to make a traditional major body-panel die is astronomical. As an extreme example, I remember a block of steel used to make the front-end section of a Ford truck cost $2 million and took two years to cool after it was cast -- in Sweden. That was in 1978 or so.
The funny thing about that one is that it was planned to stamp steel, but process changes along the way caused them to re-assign the die to forming sheet-molding compound (SMC plastic). It still cost megabucks to machine.
ok, a question for the group related to this thread
I have a 36 cadillac with badly rusted hood hinges - I've cut the rivets and have the two hinge sections sitting here - the hinge is 3 parts, a chromed center strip that runs down the center of the hood, and two chromed (and now badly rusted) side pieces, each rivited to one or the other side of the hood - I want to make/buy/cause to be made these side hinge parts - they are mostly standard sheet metal brake work, but the important part is a curl that interlocks with the center channel (like when you curl the fingers of your two hands together) - this curl holds the hood in place and also forms the hinge. I have photos, measurements, etc - everyone I've talked to says that making this is impossible, which is clearly not true since someone made them in 1936, and in fact most cars of the mid 30s use the same design so the equipment must be around there somewhere - so, how to make/where to get? Oh - hinges for Fords are available, but the ford hood is about a foot shorter (I need almost 48 inches long) so that's no good.
anyone interested in figuring this out? I can post diagrams/photos on my web site if there is interest, then maybe someone can figure this out and I can get these hinges done - it's only been 30 years now that I've been puzzling about this
Final panels are useless for tryout. Indeed, you can't even put finished panels are stage dies before the final operation (draw, trim and restrike - only the final flange die will accept a completed panel). Additionally, panels from assembled cars won't fit on any of the dies as they have been hemmed into other panels (outer panels to inner, and the reverse).
What they *are* useful for is scanning for reverse engineering. You need a CAD model of the panel before you can start making the dies.
Epoxy dies are used for springback analysis before the hard dies are even cast. Draw dies (first operation, just after the blank is cut from the roll) look only roughly like the panels that come out. Lots and lots of springback. They're trying to deal with that using FEA now, but it's not perfect. Soft tooling is still required for really screwball panel design.
Things are like door and hood outer panels aren't too bad. Designers are trying to reduce the number of panels required by basically stamping out larger panels which are more complicated. Many inner panels have very complicated geometry, the springback of which cannot be accurately predicted by FEA analysis. I worked on the current BMW X5 floor pan panel. I think the previous generation vehicle used 4+ stampings, which is now just one panel. Lots of time spent on that soft draw die.
Remember that an injection moulded part only requires one mould. A body panel requires between four and six dies, and that doesn't include the hemming dies for assembly. They weigh up to about 40 tons each, and have a maximum footprint of about 3 x 5 meters, perhaps 2 meters high when in storage. Not cheap to ship either (one or two dies per flatbed).
It's about $1 to $3 million for a set of panels, that is both hands for semetrical panels (doors, bodysides, fenders, quarter panels), inner *or* outer panels only. Inner panels are usually cheaper because the cosmetic work is not nearly as demanding, and they can frequently be hit in four operations.
I was through a prototype panel/assembly shop in Germany last year. They were using epoxy dies (not sure of the exact composition though) for the draw die, and the flanging at the end. I think they get about a hundred or so hits out of the draw before it's wrecked, as I remember.
I've never seen a panel die made of solid steel, only cast in soft gray iron (G2500 is the automotive spec, as I remember).
The only time I've seen solid block construction was for a tube hydroforming die. They clamp the two halves in a 6000-8000 ton hydraulic press during the hydroforming. As I remember, the dies are solid D2.
i just finished consulting on some hydraulic problems on a large hydroforming die that was built in piece block and had punches and cylinders imbedded in the die , the punched all the needed holes after the form was complete but before the die was opened. Tese were for nissan front subframe components
Leave it to the Times to be right on top of shit- some car mag reported on this about a year ago. They use kirksite for the dies and the productions runs will be limited to the life of one die set.
To be honest I don't have any idea. Completing the tryout on a production draw die takes thousands of man hours. I would be very interested in seeing how these guys get their dies out at a reasonable rate. Mind you, manually grinding a steel die is a lot different than manually shaping an epoxy die. And I'd be fairly surprised if their panels come out of the dies with zero (or perhaps one or two) cosmetic defects, not to mention the dimensional defects..
One thing though, once they get the die right, it can be scanned and reproduced on a mill/router fairly easily (if the original epoxy tool doesn't survive panel demand).
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